Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $171.99   8.167%   $186.0364   $186.04   $186.05   $186.00  
  Purchase #2 $238.42   5.365%   $251.2112   $251.21   $251.20   $251.20  
  Purchase #3 $53.42   11.422%   $59.5216   $59.52   $59.50   $59.50  
  Purchase #4 $58.92   13.417%   $66.8253   $66.83   $66.85   $66.80  
  Purchase #5 $129.62   12.697%   $146.0779   $146.08   $146.10   $146.10  
  Purchase #6 $54.56   13.763%   $62.0691   $62.07   $62.05   $62.10  
  Purchase #7 $230.75   13.868%   $262.7504   $262.75   $262.75   $262.80  
  7 purchase totals = $937.68       $1,034.4919   $1,034.50   $1,034.50   $1,034.50